1. Field of the Invention
The present invention relates generally to a liquid crystal display device and a driving method of the liquid crystal display device, and more particularly to an active matrix liquid crystal display device and a driving method of the active matrix liquid crystal display device.
2. Description of the Related Art
In recent years, with an increase in the range of purposes of use of liquid crystal panels, the liquid crystal displays have begun to be widely applied to vehicles with rapid prevalence (e.g. displays for navigation, and displays for rear-seat entertainment). For example, in a case where a liquid crystal panel is applied to the use in vehicles, it is required that video display be normally performed in a wide temperature range, in particular, even at very low temperatures of −30° C. to 0° C. Attention has been paid to an OCB (Optically Compensated Bend) liquid crystal mode with high responsivity characteristics, as a liquid crystal mode that is suited to operations at such very low temperatures.
In general, there is a tendency that at low temperatures the viscosity of a liquid crystal material increases and the response speed decreases. However, the OCB liquid crystal has sufficiently high responsivity characteristics for display at low temperatures, and is expected as a liquid crystal material for vehicle use.
There has been proposed a liquid crystal display device in which black display is executed at a predetermined time ratio in one frame period in order to prevent a so-called “reverse transition” phenomenon in which the liquid crystal alignment state in the OCB mode transitions reversely from a bend state to a splay state (Jpn. Pat. Appln. KOKAI Publication No. 2007-140066). In this case, at least one black signal write scan (black insertion scan) and at least one signal write scan (signal scan) are executed in one frame period.
The concept of timing setting in this method is as follows. To begin with, a basic horizontal cycle is determined, which is enough to write a non-video signal for black insertion or a video signal in one liquid crystal pixel. Thereby, a time is calculated, which is necessary for scanning a screen from its upper part to its lower part (or from its lower part to its upper part) in a black insertion write period or a video signal write period.
Next, the relative temporal relationship between the black insertion scan and the first signal write scan is determined in the following manner. If the timing of the start of black insertion scan is fixed at the beginning of the frame period, the relative temporal relationship can be varied by varying the timing of the start of signal write scan.
As the time from the start of black insertion scan (i.e. the beginning of one frame period) to the start of signal write scan is made shorter, a longer hold period (i.e. a period from the end of the first signal scan to the start of black insertion in the next frame period; the liquid crystal is kept in the signal display state) can be secured, and high luminance can be obtained. However, if this time is too short, reverse transition occurs in the OCB liquid crystal.
Taking the above into account, the time from the start of black insertion scan to the start of signal write scan is set to be as short as possible within the range in which no reverse transition occurs. In general, reverse transition tends to easily occur at high temperatures and to hardly occur at low temperatures. Thus, in accordance with temperatures, the time from the start of black insertion scan to the start of signal write scan is set to be long at high temperatures and is set to be short at low temperatures.
By driving the liquid crystal display device in the above-described manner, it is possible to perform video display which is excellent in moving image visibility in a wide temperature range including very low temperatures of −30° C. to 0° C., and is also excellent in power efficiency, luminance and contrast.
When the liquid crystal display device is driven as described above, however, vertical crosstalk appears in a displayed image in some cases.